Child objects and XML data update problem

Hi

I have an editable root object with a child list. The children are populated from xml data. When I hit save I need to rebuild the xml data from the children. The problem I'm having is with adding back items where the children are not dirty.

I can call MarkDirty in Child_Fetch but this makes the root dirty even if nothing else has changed.

I could build the whole xml from the root by looping through the child list but this is not very elegant either.

This seem like it could be a common problem. Can you tell me the best CSLA way to deal with this?

Thanks

Andrew